The present invention is a chemical reactor and method for gas phase reactant catalytic reactions.
As used herein, the term xe2x80x9cmolecular diffusionxe2x80x9d is used in its classic sense of the transfer of mass based upon Brownian motion between adjacent layers of fluid in laminar, transition, or turbulent flow, and includes transfer of mass between adjacent layers of fluid that are stagnant.
As used herein, the term xe2x80x9cKnudsen diffusionxe2x80x9d means Knudsen flow, or free molecule flow, wherein the mean free path of the molecules is long compared to a characteristic dimension of the flow field, for example the pore size of a material through which the molecules are diffusing. In Knudsen diffusion, molecules typically collide with walls rather than with other gas phase molecules.
Many catalytic reactions begin with gas phase reactants, for example steam reforming, partial oxidation, water gas shift and others. However, equipment, specifically reactor volume is generally large because of mass and heat transfer limitations. Conventional reactors are operated with a gas hourly space velocity from about 1,000 to about 3600 hrxe2x88x921. In other words, contact time is greater than 1 second because of the heat and mass transfer limitations.
These problems have been recognized and research is considering microchannel reactors because the microchannels have been shown to offer less resistance to heat and mass transfer thus creating the opportunity for dramatic reductions in process hardware volume. Several types of microchannel reactors have been described in the literature.
Franz et al., 1998 and Lowe et al., 1998 report applying a coating of the active catalyst (such as Pt, Ag, or other noble metal) directly to the microchannel wall. This approach has the disadvantage that the only usable surface area is that of the microchannel wall.
Weissmeier and Honicke, 1998a-b report creating a porous interface directly from the microchannel wall material onto which the catalyst is deposited. An aluminum wall was anodized to create the porous alumina interface that had an average pore diameter in the nanometer size range (permitting only Knudsen diffusion) and a thickness in the range of tens of microns. Disadvantages of this approach include that it is only applicable for aluminum, and limited surface area. The anodized walls formed a two-dimensional array of 700 identical microchannels.
Tonkovich/Zilka et al., 1998 reported packing catalytic powders directly within an array of parallel microchannels as a packed microbed. A disadvantage was a tendency to create relatively large pressure drops by forcing the fluid to flow through the packed microbed.
Tonkovich/Jimenez et al., 1998 reported placing a palladium catalyst supported on a metallic nickel foam within a cavity (more than an order of magnitude larger than a microchannel) and then sending the effluent to an array of microchannels to exchange heat. Again, a disadvantage was large pressure drop through the metal foam.
Hence, there is a need for a chemical reactor for catalytic reactions with fast kinetics that has a small reactor volume with a low pressure drop.
Franz, A. J., Quiram, D., Srinivasan, R., Hsing, I-M., Firebaugh, S. L., Jensen, K. F., and M. A. Schmidt, 1998, New Operating Regimes and Applications Feasible with Microreactors, Proceedings of the Second International Conference on Microreaction Technology, New Orleans, La., p 33-38.
Lowe, H., Ehrfeld, W., Gebauer, K., Golbig, K., Hausner, O., Haverkamp, V., Hessel, V., and Richter, Th., 1998, Microreactor Concepts for Heterogeneous Gas Phase Reactions, Proceedings of the Second International Conference of Microreaction Technology, March 1998, New Orleans, La., p. 63-74.
Tonkovich, A. Y., Zilka, J. L., Powell, M. R., and C. J. Call, 1998, The Catalytic Partial Oxidation of Methane in a Microchannel Chemical Reactor, Proceedings of the Second International Conference of Microreaction Technology, March 1998, New Orleans, La., p. 45-53.
Tonkovich, A. Y., Jimenez, D. M., Zilka, J. L., LaMont, M., Wang, Y., and R. S. Wegeng, 1998, Microchannel Chemical Reactors for Fuel Processing, Proceedings of the Second International Conference of Microreaction Technology, March 1998, New Orleans, La., p. 186-195.
Weissmeier, G., and Honicke, D., 1998a, Strategy for the Development of Micro Channel Reactors for Heterogeneously Catalyzed Reactions, Proceedings of the Second International Conference on Microreaction Technology, New Orleans, La., p. 24-32.
Weissmeier, G., and Honicke, D., 1998b, Microreaction Technology: Development of a microchannel reactor and its application in heterogeneously catalyzed hydrogenation, Proceedings of the Second International Conference on Microreaction Technology, New Orleans, La., p. 152-153.
The present invention provides a chemical reactor including: at least one reaction chamber comprising at least one porous catalyst material and at least one open area wherein each of said at least one reaction chamber has an internal volume defined by reaction chamber walls. The internal volume has dimensions of chamber height, chamber width and chamber length. The at least one reaction chamber comprises a chamber height or chamber width that is about 2 mm or less. At a point where the chamber height or the chamber width is about 2 mm or less, the chamber height and the chamber width define a cross-sectional area. The cross-sectional area comprises a porous catalyst material and an open area, where the porous catalyst material occupies 5% to 95% of the cross-sectional area and where the open area occupies 5% to 95% of the cross-sectional area. The open area in the cross-sectional area occupies a contiguous area of 5xc3x9710xe2x88x928 to 1xc3x9710xe2x88x922 m2 and the porous catalyst material has a pore volume of 5 to 98% and more than 20% of the pore volume comprises pores having sizes of from 0.1 to 300 microns.
In another aspect, the invention provides a chemical reactor including at least one reaction chamber in which there are catalyst rods, plates or baffles having a length to thickness ratio of at least 10, and wherein the at least one reaction chamber has an internal volume defined by reaction chamber walls. The internal volume has dimensions of chamber height, chamber width and chamber length; and the at least one reaction chamber comprises a chamber height or chamber width that is 2 mm or less. The catalyst rods, plates or baffles are disposed in said reaction chamber such that the pressure drop across the reaction chamber is less than 20% of the total system inlet pressure.
In another aspect, the invention provides a chemical reactor including at least three layers. A first layer comprising a first porous catalyst material; a second layer comprising a heat exchanger and at least one fluid flow path through the second layer. The second layer is disposed in the reaction chamber such that fluid passing through the first porous catalyst material can pass through the at least one fluid flow path, and a third layer comprising a second porous catalyst material where the third layer is disposed in the reaction chamber such that fluid passing through the second layer can pass into the second porous catalyst material. The first layer includes continuous channels having dimensions of channel height, channel width and channel length. The continuous channels have a channel height and/or channel width of 0.1 micrometer to 2 mm or less. The first porous catalyst material has a pore volume of 5 to 98% and more than 20% of the pore volume comprises pores having sizes of from 0.1 to 300 microns.
The invention also includes a method of hydrocarbon steam reforming. In this method, a reactant stream comprising steam and hydrocarbon is passed into at least one reaction chamber. The reaction chamber has an internal volume having dimensions of chamber height, chamber width and chamber length. The chamber height or chamber width is 2 mm or less. Each reaction chamber has a beginning and an end. The chamber length is the distance from the beginning to the end of the reaction chamber. The reactant stream entering the beginning of the reaction chamber is converted to a product stream that exits the reaction chamber. This product stream includes hydrogen, carbon dioxide and/or carbon monoxide; wherein at least 70% of said equilibrium conversion of the hydrocarbon entering the beginning of said at least one reaction chamber is converted to hydrogen, carbon monoxide and/or carbon dioxide. The process is conducted under conditions such that the hydrocarbon has a contact time of less than 300 milliseconds.
The invention further provides a method of conducting a chemical reaction in a chemical reactor. In this method, gaseous reactant is passed into a first compartment. The chemical reactor includes a porous catalyst material, a first compartment and a second compartment. The first compartment and the second compartment include open spaces that permit bulk flow of a gas. The first compartment has an internal volume having dimensions of compartment height, compartment width and compartment length. The compartment height or width is about 2 mm or less. The porous catalyst material is disposed between the first compartment and the second compartment. The gaseous reactant reacts within the porous catalyst material.
In another aspect, the invention provides a method of conducting a chemical reaction in a chemical reactor in which a gaseous reactant is passed into a first compartment. The reaction chamber comprises a first compartment and a second compartment, and a partition disposed between the first compartment and the second compartment. The partition comprises a fluid distribution layer or a separating agent. The first compartment has an internal volume having dimensions of compartment height, compartment width and compartment length. The first compartment includes a porous catalyst material and at least one open space that permits bulk flow of a gas and has a compartment height or compartment width that is about 2 mm or less. In this method a gas travels through the partition. In preferred embodiments, the partition includes a flow distribution layer and a gaseous reactant convectively travels through the flow distribution layer from the second to the first compartment; and after traveling through the flow distribution sheet, reacts in a porous catalyst material contained within the first compartment. In another embodiment, the partition comprises a membrane or a sorbent which may selectively separate a product formed in the first compartment or selectively separate a reactant such as oxygen from air for use in a distributed feed application.
The invention also includes a method of conducting a chemical reaction in which a gaseous reactant is passed into a bulk flow path of at least one reaction chamber. The bulk flow path is contiguous throughout said chamber length. The reaction chamber has an internal volume having dimensions of chamber height, chamber width and chamber length. The at least one reaction chamber comprises a chamber height or chamber width that is about 2 mm or less. A porous catalyst material is disposed within said internal volume, the porous catalyst material having a porous internal structure such that the gaseous reactant can diffuse molecularly within the material. The gaseous reactant reacts in the porous catalyst material to form at least one product.
While various aspects of the present invention are described and claimed in terms of one or two reaction chambers, it should be recognized that the invention is envisioned to operate most effectively where reactors contain multiple reaction chambers, and therefore the invention should not be limited to reactors and methods having only one reaction chamber. In many embodiments a characteristic dimension of about 2 mm or less is selected because mass transport and heat transport on this scale can be highly efficient.
It should be recognized that many of the embodiments and reaction chamber designs described herein are well-suited for combinations amongst the various designs. For example, the reaction chambers illustrated in FIGS. 10d and 10e could be integrated with a conduit for carrying fluids from one layer to another (such as a conduit from a second catalyst layer back to the first catalyst layer). Therefore the invention should be understood as including combinations of the various designs and embodiments described herein.
The subject matter of the present invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. However, both the organization and method of operation, together with further advantages and objects thereof, may best be understood by reference to the following description taken in connection with accompanying drawings wherein like reference characters refer to like elements.